1. Field of the Invention
The present invention relates generally to the field of motors, and more particularly, but not by way of limitation, to the field of fluid pressure operated linear reciprocating motors.
2. Description of the Prior Art
Bias spool valves have long been used to operate fluid pressure operated linear reciprocating motors. Such motors usually have a piston that is reciprocated by the application of constant pressure against a first pressure face at one end of the piston and a variable fluid pressure against a second pressure face at the other end of the piston, the first and second pressure faces being of different areas so as to present a differential pressure force thereagainst. This is sometimes designated a differential type piston motor. In order to move the piston, of course, fluid pressure must be varied against one of the pressure faces, and this is usually the larger of the pressure faces. Early prior art devices selectively manipulated the fluid pressure by external valving means. However, with the invention of the bias spool valve, a device was available for an internally disposed, fluid actuated valving mechanism for varying the pressure against the larger pressure face. Various designs have been proposed for porting fluid to the piston, the bias valve spool serving to selectively port the fluid pressure to the piston pressure faces while the spool itself being selectively positioned by the fluid pressure action thereupon. As its name implies, the valve spool also is manipulated by varying the pressure against differential pressure faces disposed thereon.
As the valve spool moves in a typical fluid motor, it serves to open and close fluid ports, thereby selectively routing the pressure fluid in a manner that varies the pressure against the piston pressure faces. In some designs, the spool or the piston physically moves a member in relation to the fluid passageways, and in other designs the spool selectively blocks the fluid passageways.
Due to the cycling rate required in most fluid motor applications, any physical contact or impact between moving components is undesirable, as this leads to deterioration and subsequent reduction of unit efficiency and life expectation. In prior art devices, it has usually been necessary to limit the cycling rate below the unit's potential rate in order to strike a working balance between power output and unit deterioration. Even so, such prior art units offer low operating efficiencies of power transfer usually in the order of 20% or less.
Prior art units, along with their low efficiencies, have been known to create a great deal of objectionable noise. This is due to the high rate of fluid through-put required to generate a given power output, as well as the noise generated due to mechanical impact of moving components.